An archosauromorph reptile fossil preserving a live birth rewrites understanding of reproductive evolution

A remarkable 250 million-year-old "terrible-headed lizard" fossil found in China shows an embryo inside the mother—clear evidence for live birth! This research, recently published in the journal Nature Communications, is part of an ongoing collaboration between palaeontologists in China, the United States, the UK and TeBi Researcher Professor Jonathan Aitchison, Australia. Professor Jonathan Aitchison, co-author, said the fossil unexpectedly provided the first evidence for live birth in an animal group previously thought to exclusively lay eggs.

"Further evolutionary analysis revealed the first case of live birth in such a wide group containing birds, crocodilians, dinosaurs and pterosaurs among others, and pushes back evidence of reproductive biology in the group by 50 million years," Professor Jun Liu said.

This pregnant Dinocephalosaurus could help corroborate a dominant idea about what makes a reptile stop laying eggs and start birthing live young: that viviparity is an adaptation necessary for reptiles to move to a fully aquatic lifestyle. 

"Because eggs of reptiles (and birds) cannot be laid in water, aquatic reptiles have two choices: they either must come to land to lay their eggs (like sea turtles) or they must be viviparous (like ichthyosaurs and certain sea snakes)," Blackburn explains. "Dinocephalosaurus is highly specialized for aquatic life and probably could not come onto the land to lay its eggs."


Read the paper here: http://www.nature.com/articles/ncomms14445

 ( a ) Photograph. The three separate blocks are arranged following their original positions in the field. ( b ) Interpretive drawing. Dotted line indicates the rough course of the vertebral column of the adult. The different colour in the cervical region aims to facilitate the association of cervical ribs with corresponding vertebrae. ( c ) Photo showing a close-up of the embryo preserved in the stomach region of LPV 30280. ( d ) Interpretive drawing of the embryo. ( e ) Photo showing a close-up of the perleidid fish preserved in the stomach region of LPV 30280. ( f ) Artist's reconstruction of  Dinocephalosaurus  showing the rough position of the embryo within the mother. ax, axis; car, caudal rib; crh, cervical rib head; cv, cervical vertebrae; d4, fourth digit; f, perleidid fish; fe, femur; fi, fibula; h, humerus; ha, haemal arch; m, mandible; mt1, metatarsal 1; mt5, metatarsal 5; poz, postzygapophysis; prz, prezygapophysis; ra, radius; ti, tibia; ul, ulna. Scale bar, 20 cm.

(a) Photograph. The three separate blocks are arranged following their original positions in the field. (b) Interpretive drawing. Dotted line indicates the rough course of the vertebral column of the adult. The different colour in the cervical region aims to facilitate the association of cervical ribs with corresponding vertebrae. (c) Photo showing a close-up of the embryo preserved in the stomach region of LPV 30280. (d) Interpretive drawing of the embryo. (e) Photo showing a close-up of the perleidid fish preserved in the stomach region of LPV 30280. (f) Artist's reconstruction of Dinocephalosaurus showing the rough position of the embryo within the mother. ax, axis; car, caudal rib; crh, cervical rib head; cv, cervical vertebrae; d4, fourth digit; f, perleidid fish; fe, femur; fi, fibula; h, humerus; ha, haemal arch; m, mandible; mt1, metatarsal 1; mt5, metatarsal 5; poz, postzygapophysis; prz, prezygapophysis; ra, radius; ti, tibia; ul, ulna. Scale bar, 20 cm.